In an inorganic fiber mat made of an inorganic fiber such as glass wool or rock wool, a phenolic resin binder containing as a main component a phenol-formaldehyde resin (or resol-type phenolic resin) has been widely used as a binder for bonding fibers with each other. The phenolic resin binder described above is heat-cured within a relatively short time to provide a cured product having strength, and hence the inorganic fiber mats using the phenolic resin binder are excellent in performance such as shape retention, thickness restoring property after opening compression baling, or deflection resistance.
However, formaldehyde is released from the inorganic fiber mat using the phenolic resin binder during the production process, particularly at the time of binder curing. Thus, treating or coping with the released formaldehyde remains as a problem. In recent years, restriction of the amount of formaldehyde emission by laws and regulations or the like has been particularly demanded from the viewpoint of reducing environmental load.
In order to suppress emission of aldehydes released from an inorganic fiber mat, there is a method of applying an aldehyde scavenger to an inorganic fiber mat after binder curing. Patent Document 1 discloses a method of producing an inorganic fiber heat insulating material, the method including a fiber collection step of adding a binder to inorganic fibers and accumulating in a mat-like shape to form an inorganic fiber web, a curing step of curing the binder on the inorganic fiber web to form an inorganic fiber mat, and a step of spraying and applying a solution of a formaldehyde scavenger as mist-like droplets having an average diameter of 1 to 20 μm to the inorganic fibers in a mat-like shape after the fiber collection step.    Patent Document 1: JP 2007-92822 A